Adenocarcinoma of the prostate metastasizes to the skeleton where it commonly produces predominantly osteoblastic rather than osteolytic lesions. These metastases are associated with increased osteoblast numbers and activity. Previous studies have isolated a growth factor for osteoblast-like cells from conditioned media of a human prostate cancer cell line which was identified as the amino terminal fragment (ATF) of urokinase-type plasminogen activator (uPA), a fragment containing an EGF- like domain. The hypothesis to be tested in this application is that over production or persistence of ATFs containing this growth factor domain is important in the pathogenesis of osteoblast metastases by prostatic cancer, whereas secretion of the proteolytic domain of uPA contributes to bone matrix lysis by the invading tumor. To test this hypothesis the applicant will examine the spectrum of anabolic actions, bio-potency and mechanism of anabolic action of molecular forms of uPA on skeletal tissue in vitro. Recombinant forms of human and rat uPA will be tested as well as analogues of uPA prepared by site-directed mutagenesis. In addition to determining effects on receptor binding and growth of osteoblastic cells, the applicant will assess effects on post-receptor signaling or indices of differentiation and, on in vitro mineralization and osteoblastic cultures. The cloning of the human and rat skeletal uPA receptors will be completed and expression studies will be performed. In a second series of studies, gene transfer methods will be used to develop variants of a rat prostatic cancer which over-expressed uPA or ATF, or which fail to express uPA. These variants will be used to explore the development of osteoblastic or osteolytic metastases in vivo. This proposal seeks to determine whether discrete molecular domains of uPA are involved in osseus growth vs. osseus breakdown.